High voltage power vacuum fuse

ABSTRACT

A power vacuum fuse for interrupting high voltage alternating currents. The fuse has one or more fusible, current-responsive elements spanning a pair of spaced electrodes adjacent the peripheries thereof. Leads to a high voltage line extend from the central regions of the electrodes, each of the electrodes being slotted from the central region to the periphery thereof to define a current path to each element which extends both radially outwardly and tangentially with respect to a central axis of the electrodes. The effect of the slotted electrodes is to apply a force to each element which expels it from between the electrodes upon melting of the element, such force having a tangential component which spins the arc established when all the elements are severed, thereby preventing the arc from swelling to preclude extreme volatilization of the elements and electrodes so that the circuit will be interrupted at the first natural current zero following severance of the elements.

United States Patent [72] Inventor Thomas E. Curtis Centralia,Mo. [21]AppLNo. 814,736 [22] Filed Apr. 9,1969 [45] Patented June 22,1971 [73]Assignee A. B. Chance Company Centralia,Mo.

[54] HIGH VOLTAGE POWER VACUUM FUSE 8 Claims, 6 Drawing Figs. 52u.s.ct... 337/273 [51] 1nt.Cl ..110lh85/38 [50] FieldotSearch 337/161,246, 273, 278, 279, 281, 282; ZOO/144.2

[56] References Cited UNITED STATES PATENTS 3,287,525 11/1966 Mikulecky337/161 3,246,979 4/1966 Lafferty etal... .200/144.2(UX) 2,854,5519/1958 Lange 337/282(X) 1,757,397 5/1930 Sorensen etal 337/246 $1 1 w\j, i

l 1,3,ss7,024

Primary Examiner Bernard A. Gilheany Assistant Examiner-Dewitt M. MorganAttorney-Schmidt, Johnson, Hovey, Williams & Chase ABSTRACT: A powervacuum fuse for interrupting high voltage alternating currents. The fusehas one or more fusible, current-responsive elements spanning a pair ofspaced electrodes adjacent the peripheries thereof. Leads to a highvoltage line extend from the central regions of the electrodes,

each of the electrodes being slotted from the central region to theperiphery thereof to define a current path to each element which extendsboth radially outwardly and tangentially with respect to a central axisof the electrodes. The effect of the slotted electrodes is to apply aforce to each element which expels it from between the electrodes uponmelting of the element, such force having a tangential component whichspins the are established when all the elements are severed, therebypreventing the are from swelling to preclude extreme volatilization ofthe elements and electrodes so that the circuit will be interrupted atthe first natural current zero following severance of the elements.

PATENTED JUH22 19m INVENTOR 7770/7ms E. aunf fg ATTORNEY5 HIGH VOLTAGEPOWER VACUUM FUSE This invention relates to improvements in power vacuumfuses and, in particular, to a vacuum fuse incorporating means forpreventing the are established during interruption from causing extremevolatilization of the fuse material.

One of the problems found in vacuum fuses in high voltage, high amperageapplications is the extreme volatilization of the electrodes andcurrent-responsive elementor elements of the fuse when interruption iscaused by high short circuit currents. Although ahigh vacuum conditionmay be maintained within the fuse prior to interruption, additional ionsare made available to sustain an electric are if substantialvolatilization is per mitted to occur at the time of interruption.Manifestly, complete interruption of the circuit is not effected untilthe arc is extinguished and, secondly, the prolonged presence of the arcpresents ahazard which must be avoided.

It is, therefore, the primary object of this invention to provide apower vacuum'fuse which will operate at voltages on the order of 600volts and higher with assurance that. an arc will not be long sustainedwithin the fuse at the time that the fusible element or elements thereofare severed by a high short circuit current.

As a corollary to the foregoing object, it is an important aim of thepresent inventionto provide a fuse as aforesaid which effects'rapidmovement of the are upon establishment thereof to prevent the are fromdwelling and thereby causing extreme volatilization of surroundingmaterial.

Furthermore, it is an important object of this invention to provide afuse as aforesaid having electrodes between which a fusible elementextends adjacent the peripheries of the electrodes, wherein suchelectrodes cause the current to apply a force to the element having bothradially and tangentially directed components so that the element uponmelting thereof will be expelled from between the electrodes by theforce and the arcthus established will be moved along the electrodes'ina spinning fashion by the tangential force component to prevent the arcfrom dwelling where initially established.

Another important object of the invention is to provide a fuse asaforesaid having a plurality of such current-responsive elements,wherein progressively longer paths for current flow from the centralregions of the electrodes to successive elements are provided, andwherein such paths extend both radially outwardly and tangentially withrespect to a central axis of the electrodes to effect the application ofboth radial and tangential force components to the elements.

Still another important'object of the invention is to provide a powerfuse as aforesaid in which the same components of the fuse constructionmay be utilized for different ampere ratings, with the exception of onlythe current-responsive element or elements which would be sized inaccordance with the desired continuous current rating.

Yet another important object of the invention is to provide a vacuumfuse construction having novel means of connecting the fusible elementsto the electrodes so that elements of any of a number of diameters(depending upon the desired rating) may be utilized with the sameelectrode configurationQ In the drawing:

FIG. I is a cross-sectional view of the power fuse showing theelectrodes and the leads extending therefrom in elevation;

FIG. 2 is an enlarged, fragmentary view showing the electrodes inperspective;

FIG. 3 is a top plan view of the upper electrode on the same scaleasFIG.2;

FIG. 4 is a view half in cross section and half in elevation of thelower electrode on the same scale as FIG. 2;

FIG. 5 is a cross-sectional, detail view taken along line 5-5 providedfor this purpose. A vacuum in chamber 18 on the order of 10" to 1'0"Torr is established, and the chamber 18 is then sealed such as bypinching the tube 20 shut as illustrated. A conductive probe 22. insidewall 12 is provided so that the vacuum in chamber 18 may be checkedelectrically.

A pair of upper and lower, disc-shaped electrodes 24 and 24a aredisposedin chamber 18 in spaced, axially aligned relationship to each other. Thetwo electrodes 24 and 24a are identical in configuration with one beinginverted with respect to the other. Therefore, it will be understoodthat corresponding features of the two electrodes are designated by thesame reference numerals with the addition of the a" notation withreference to the lower electrode'24a.

The electrodes 24 and 240 have central regions 26 and 26a to which apair of solid copper leads 28 and 28a are joined both mechanically andelectrically at their respective lower and upper ends. As is clear inFIG. 4, the upper end of the lead 28aisflush with region 26a, the latterbeing axially bored and countersunk to receive the head of a flat headscrew 27a which is threaded into a tapped, axial hole in the end of lead284. The lead 28 is joined to the electrode 24 in the same manner andextends outwardly from the housing 10 through the end plate 14, the lead28 being connected to a high voltage line (not shown) to be protected bythe fuse. The lead 28a from the lower electrode 24a extends through theend plate 16 and is also connected to the line to place the fuse inseries therewith. Alternatively, the leads 28 and 28a may be silversoldered to the electrodes 24 and 24a and the screw holes omitted.

Three generally spiral slots 29, 30 and 31 in electrode 24 extend fromthe central region 26 thereof radially and tangentially outwardly to thecircumferential periphery 32 of the electrode 24. The inner and outerterminations of the three slots 29, 30 and 31 are angularly spaced atintervals of l20, and adjacent slots partially angularly overlap eachother as is clear in FIG. 3.

Three fusible, rodlike elements 34, 36 and 38, which may be of coppercomposition, span the electrodes 24 and 24a and are disposed adjacentthe peripheries 32 and 32a thereof generally alongside the slot 30. Theelements 34, 36 and 38 are equally angularly spaced'about the commoncentral axis 40 of the electrodes 24 and 24a defined by their geometriccenters. Three hollow bosses 42, 44 and 46 project from the uppersurface of the electrode 24 and are aligned with three openings in theelectrode 24 into which the upper end portions of the elements 34, 36and 38 extend respectively. One of such openings 48 aligned with theboss 42 is revealed in FIG. 5, where it may be seen that the element 34is of lesser diameter than the opening 48 and extends thereintocompletely through the electrode 24' and into the boss 42. To effectboth an electrical and a mechanical connection, the boss 42 is crimpedaround the tip of the upper end portion of element 34, the other bosses44 and 46 being likewise crimped around the upper tips of theirrespective elements 36 and 38. In similar fashion the bosses 42a, 44aand 46a on the electrode 240 are crimped around the lower tips ofrespective elements 3438.

A cylindrical support spacer 50 of insulating material, preferably aceramic substance, is interposed between the electrodes 24 and 24a andis disposed in coaxial relationship to the axis 40. The spacer 50 isradially inwardly spaced from the elements 34, 36 and 38, as is mostclearly revealed in FIG. I, and is useful in assembly operations.

A cylindrical, metallic shield 52 is coaxially disposed within housinglo and is radially outwardly spaced from the electrodes 24 and 24a andradially inwardly spaced from the housing sidewall 12. The shield 52 isattached to the endplate l4 and extends into surrounding relationship tothe electrode assembly to protect the sidewall 12 during interruption ofthe fuse, as will be discussed hereinafter.

The present invention is especially adapted for the protection ofalternating current power lines having voltages on the order of 600volts through the high voltage range. The leads 28 and 28a are connectedto the line to be protected to place the elements 34, 36 and 38 inseries with such line. FIG. 3 illustrates the current paths to the threeelements 34, 36 and 38 which extend from the central region 26 of theelectrode 24 around the slot 30. Identical current paths also existbetween the central region 26a of the lower electrode 24a and theelements 34, 36 and 38, except that the direction of current flow isopposite during a given half cycle of the alternating current wave.

The current path along electrode 24 to the element 34 is represented at54 and is a straight line from the inner termination of the slot 30 tothe upper tip of the element 34 where the connection is made to theelectrode 24. The current path to the element 36 is represented at 56and follows the outer edge of the slot 30 until the latter diverges froma direct line to the element 36, at which point the path 56 follows astraight line from the bend in the slot 30 to the element 36. Similarly,the current path 58 to the'third element 38 follows the slot 30 forapproximately two-thirds of its length before traversing a straight lineto the element 38. It may be appreciated, therefore, that the spiralconfiguration of the slot 30 forces the current paths 54, 56 and 58 toextend in both radial and tangential directions with respect to thecentral axis 40 in order to reach the respective elements by theshortest route. F urthermore, it is important to note that the currentpaths 54, 56 and 58 to the respective elements 34, 36 and 38 areprogressively longer in length, asis' clear from a study of H0. 3.

When a short circuit or overload current flows through the fuse, thepaths 54, 56 and 58 are necessarily traversed by the current to causethe current to apply electromagnetic forces to the three elements. Theresultant force on the element 36 is represented by the vector R,, theresultant force on the element 36 is represented by the vector R,, andthe resultant force on the element 38 is represented by the vector R,.Each of these vectors has both radial and tangential force components asis .clearly illustrated in the vector diagrams included in FIG. 3. Aseach element 34, 36 or 38 melts, the presence of the resultant vectorR,, R, or R expels the element from between the electrodes 24 and 24a byejection therefrom in a direction toward the shield 52 (FIG. 1). Thus,the melted material of the current-responsive elements is not permittedto remain between or on the electrodes where substantial volatilizationthereof could occur when arcing across the electrodes is ultimatelyproduced upon severance of all of the elements.

The tangential force components are identified P,, P, and P and serve tospin the are about the axis 40 to further reduce the volatilization ofthe fusible elements and also prevent excessive volatilization of theelectrode material. This spinning persists until a natural current zerooccurs following severance of the three elements. This action will nowbe explained in greater detail.

Besides the tangential force components P,, P and P forces of mutualattraction between the elements 34, 36 and 38 are present prior toseverance of the elements by the melting thereof. Thus,- an attractiveforce exists between elements 34 and 36, a second attractive forceexists between elements 36 and 38, and, a third attractive force is inexistence between elements 34 and 38. Therefore, the total force onelement 34 is the vectorial sum of R (including its tangential componentP,) and the mutual forces of attraction between element 34 and elements36 and 38. It is believed that this total force on element 34 is thegreatest total force experiencedrby any of the elements. This conclusionis reached sinc e,.-- .prior to severance of any element, the forces ofmutual attraction on the center element 36 cancel one another and theresultant mutual attraction force on the element 38 is the vectorial sumof the mutual attraction force between elements 34 and 38 and the mutualattraction force between elements 36 and 38, both of which areessentially in opposition to the force R in contrast to this, the forceR, and the mutual attraction forces acting on element 34 are vectoriallyadditive, resulting in a higher total force on element 34.

ln accordance with the foregoing, it is believed that when the element34 reaches a plastic state, due to the flow of short circuit or overloadcurrent therethrough, this element is severed first because of thehigher total force acting thereon in a direction transverse to itslength. This increases the currents through the remaining elements 36and 38. The total force on the element 36 now becomes a vectorialcombination of R, and the mutual attraction force'between elements 36and 38; therefore, the element 36 is the next to sever. With element 36now severed, the entire current must flow through the single remainingelement 38, which severs immediately due to the high force of R actingthereon. The severance of all three elements occurs very rapidly and, ifthe short circuit condition occurs as the current wave is ascending,complete severance of all elements should be effected prior to the timethat the current wave reaches the next natural current zero, with fullinterruption of the circuit occurring at the current zero point.

In order for interruption to occur, the are that will be establishedacross the electrodes 24 and 24a at the time of severance of the lastelement must be extinguished. Due to the presence of the tangentialforce component P,-,, the arc is forced to move along the periphery ofthe electrodes and is thus spun about the central axis 40. The presenceof tangential forces to maintain the arc in motion is assured by thespiral configuration of the slots 29, 30 and 31, the latter serving tomaintain atangential driving force on the are at all angular positionsthereof to sustain the spinning motion. Therefore, substantialvolatilization of the electrode material, as well as the elements 34-38,is precluded since the arc is prevented from dwelling where initiallyestablished. The spinning motion of the arc continues until the currentzero is reached, whereupon extinguishment of the arc completes theinterruption of the circuit. I

As may now be appreciated, the material of the electrodes 24 and 24ashould, as much as possible, be resistant to volatilization to minimizethe generation of gaseous ions during interruption. Annealed copper issuitable as the electrode material and should be baked out at asufficient temperature to remove occluded gases which could interferewith the interruption of the fuse.

Although three fusible elements 34--38 are illustrated herein, it shouldbe understood that one or a plurality of such elements may be utilizedin accordance with the continuous rating desired for a particular fuseapplication. In this respect, it is noteworthy that the construction ofthe fuse of the present invention is such that fuses of differentratings may be constructed utilizing the same basic components withoutmodification, except for the number, size and material of the fusibleelements themselves. The adaptation of elements of different diametersto a single electrode design is best illustrated in FIG. 5, where it maybe seen that elements of different diameters may be inserted into therespective openings therefor in the electrodes. The opening 48 thereillustrated would be of a diameter greater than the maximum diameter ofthe fusible elements to be utilized, and the internal diameter of thehollow boss 42 (prior to crimping) would be at least equal to suchmaximum diameter. If desired, as shown in FIG. 6, a ceramic insulatingsleeve 60 may be inserted into an enlarged opening 48' to positivelyprevent contact of the element 34 with the electrode 24 beneath theupper tip of the element as it bends during severance.

Although the electrode configuration herein is one in which a pluralityof generally spiral slots are employed, it should also be understoodthat other slotted electrode configurations could be utilized toestablish the requisite radial and tangential force components.Regardless of the particular slot arrangement utilized, however, it isimportant that the radial and tangential force components produced as aresult of the slotted configuration have sufficient magnitude to executethe element-ejecting and arc-spinning functions discussed above.Otherwise, the problem of excessive volatilization becomes acute, andthefuse would not be suited to the high voltage, high power applicationsfor which the present invention is particularly adapted. Although theadvantageous features of the fuse are useful at voltages as low as 600volts, special need for the invention is particularly experienced atline voltages on the order of 5,000 volts and above.

Having thus described the invention, what I claim as new and desired tobe secured by Letters Patent is:

l. A power fuse comprising: housing structure having an evacuatedchamber therein; a pair of spaced electrodes in said chamber; a fusible,current-responsive element extending between said electrodes andelectrically interconnecting the latter; and means for electricallyconnecting said electrodes with a current-carrying line to interposesaid element in series with said line, I said electrodes havingnonradial groove defining means therein configured to cause currentflowing between said electrodes through said element to apply a force tothe element in a direction to both i a. expel the element from betweenthe electrodes upon melting of the element under short circuit currentconditions and attendant establishment of an arc across the electrodes,and

b. effect movement of the are along the electrodes to prevent the arcfrom dwelling where initially established or at any point thereon,

each of said electrodes having an outer periphery,

said connecting means being connected to a region of each electrodedisposed centrally with respect to the periphery thereof,

the central regions of said electrodes being aligned to define an axisextending between the electrodes through said regions,

said element spanning said electrodes adjacent the peripheries thereofin spaced relationship to said regions and interconnecting opposedportions of the electrodes which are in closest relative spacedrelationship,

said force having components directed radially outwardly of said axisand tangentially thereof respectively, whereby the force effects theexpulsion of the melted element and the tangential component thereofimparts said movement to the arc and spins the latter about said axis.

2. The power fuse as claimed in claim 1,

said element being rodlike and having a diameter selected in accordancewith the desired continuous current rating of the fuse,

each of said electrodes havingan opening therein adjacent the peripherythereof of a diameter greater than the diameter of the element thatwould be selected for the maximum rating of the fuse,

said element having opposed end portions extending into respectiveopenings,

each of said electrodes having means adjacent its opening connecting theend portion therein to the electrode.

3. The power fuse as claimed in claim 2,

each of said electrodes having a hollow boss thereon aligned with theopening therein for receiving the respective end portion,

the boss of each electrode being crimped around the received end portionto present said end portion connecting means.

4. The power fuse as claimed in claim 1;

and a generally cylindrical support, spacer of insulating materialdisposed between said electrodes in coaxial relationship to said axisand radially inwardly of said element.

5. The power fuse as claimed in claim 1;

and a shield radially spaced from said axis and disposed in surroundingrelationship to said electrodes between the latter and said housing.

6. The power fuse as claimed in claim I,

each of said electrodes having slot means therethrough presenting saidgroove means causing current to apply said force to said element, saidslot means extending along an arcuate path from said region of eachelectrode outwardly to said periphery thereof and establishing anonlinear path for current flow from said region to said elementextending both radially outwardly of said axis and tangentially thereofto thereby eflect application of said force to said element, wherebysaid force effects the expulsion of the melted element and has atangential component which imparts said movement to the arc and spinsthe latter about said axis. 7. A power fuse comprising: housingstructure having an evacuated chamber therein; a pair of spacedelectrodes in said chamber each having an outer periphery; a pluralityof fusible, current-responsive elements extending between saidelectrodes and electrically interconnecting the latter; and v means forelectrically connecting said electrodes with a current-carrying line tointerpose said elements in series with said line, said connecting meansbeing connected to a region of each electrode disposed centrally withrespect to the periphery thereof, the central regions of said electrodesbeing aligned to define an axis extending between the electrodes throughsaid regions, said elements being angularly spaced from one another withrespect to said axis and spanning said electrodes adjacent theperipheries thereof in spaced relationship to said regions andinterconnecting opposed portions of the electrodes which are in closestrelative spaced relationship, said electrodes having nonradial groovedefining means configured to cause current flowing between saidelectrodes through said elements to apply forces to respective elementshaving components directed radially outwardly of said axis andtangentially thereof to both a. expel the elements from between theelectrodes as the elements melt under short circuit current conditions,whereby an arc is established across the electrodes when all of theelements are expelled, and

b. spin the are about said axis to prevent the are from dwelling whereinitially established or at any point on the electrodes.

8. The power fuse as claimed in claim 7,

each of said electrodes having slot means therethrough presenting saidgroove means causing current to apply said forces to said elements, saidslot means extending along an arcuate path from said region of eachelectrode outwardly to said periphery thereof and establishingprogressively longer paths for current flow from said re gion tosuccessive elements,

said paths extending both radially outwardly and tangentially of saidaxis to effect application of said force components to said elements.

1. A power fuse comprising: housing structure having an evacuatedchamber therein; a pair of spaced electrodes in said chamber; a fusible,current-responsive element extending between said electrodes andelectrically interconnecting the latter; and means for electricallyconnecting said electrodes with a current-carrying line to interposesaid element in series with said line, said electrodes having nonradialgroove defining means therein configured to cause current flowingbetween said electrodes through said element to apply a force to theelement in a direction to both a. expel the element from between theelectrodes upon melting of the element under short circuit currentconditions and attendant establishment of an arc across the electrodes,and b. effect movement of the arc along the electrodes to prevent thearc from dwelling where initially established or at any point thereon,each of said electrodes having an outer periphery, said connecting meansbeing connected to a region of each electrode disposed centrally withrespect to the periphery thereof, the central regions of said electrodesbeing aligned to define an axis extending between the electrodes throughsaid regions, said element spanning said electrodes adjacent theperipheries thereof in spaced relationship to said regions andinterconnecting opposed portions of the electrodes which are in closestrelative spaced relationship, said force having components directedradially outwardly of said axis and tangentially thereof respectively,whereby the force effects the expulsion of the melted element and thetangential component thereof imparts said movement to the arc and spinsthe latter about said axis.
 2. The power fuse as claimed in claim 1,said element being rodlike and having a diameter selected in accordancewith the desired continuous current rating of the fuse, each of saidelectrodes having an opening therein adjacent the periphery thereof of adiameter greater than the diameter of the element that would be selectedfor the maximum rating of the fuse, said element having opposed endportions extending into respective openings, each of said electrodeshaving means adjacent its opening connecting the end portion therein tothe electrode.
 3. The power fuse as claimed in claim 2, each of saidelectrodes having a hollow boss thereon aligned with the opening thereinfor receiving the respective end portion, the boss of each electrodebeing crimped around the received end portion to present said endportion connecting means.
 4. The power fuse as claimed in claim 1; and agenerally cylindrical support spacer of insulating material disposedbetween said electrodes in coaxial relationship to said axis andradially inwardly of said element.
 5. The power fuse as claimed in claim1; and a shield radially spaced from said axis and disposed insurrounding relationship to said electrodes between the latter and saidhousing.
 6. The power fuse as claimed in claim 1, each of saidelectrodes having slot means therethrough presenting said groove meanscausing current to apply said force to said element, said slot meansextending along an arcuate path from said region of each electrodeoutwardly to said periphery thereof and establishing a nonlinear pathfor current flow from said region to said element extending bothradially outwardly of said axis and tangentially thereof to therebyeffect application of said force to said element, whereby said forceeffects the expulsion of the melted element and has a tangentialcomponent which imparts said movement to the arc and spins the latterabout said axis.
 7. A power fuse comprising: housing structure having anevacuated chamber therein; a pair of spaced electrodes in said chambereach having an outer periphery; a plurality of fusible,current-responsive elements extending between said electrodes andelectrically interconnecting the latter; and means for electricallyconnecting said electrodes with a current-carrying line to interposesaid elements in series with said line, said connecting means beingconnected to a region of each electrode disposed centrally with respectto the periphery thereof, the central regions of said electrodes beingaligned to define an axis extending between the electrodes through saidregions, said elements being angularly spaced from one another withrespect to said axis and spanning said electrodes adjacent theperipheries thereof in spaced relationship to said regions andinterconnecting opPosed portions of the electrodes which are in closestrelative spaced relationship, said electrodes having nonradial groovedefining means configured to cause current flowing between saidelectrodes through said elements to apply forces to respective elementshaving components directed radially outwardly of said axis andtangentially thereof to both a. expel the elements from between theelectrodes as the elements melt under short circuit current conditions,whereby an arc is established across the electrodes when all of theelements are expelled, and b. spin the arc about said axis to preventthe arc from dwelling where initially established or at any point on theelectrodes.
 8. The power fuse as claimed in claim 7, each of saidelectrodes having slot means therethrough presenting said groove meanscausing current to apply said forces to said elements, said slot meansextending along an arcuate path from said region of each electrodeoutwardly to said periphery thereof and establishing progressivelylonger paths for current flow from said region to successive elements,said paths extending both radially outwardly and tangentially of saidaxis to effect application of said force components to said elements.